Forecasts designed for aviation users have been divided into Tactical (0-2 hr) and Strategic (2-6 hr) time domains. Within the tactical domain, both Deterministic and Probabilistic forecasts are in use for aviation, and there has been some confusion about how they differ and which is better.

In this paper we explain the difference between the deterministic and probabilistic forecasts, illustrate their use in both the tactical and strategic domains with examples run on the same data cases, and compare them with truth to illustrate the pros and cons of each.

The forecasts being compared are the deterministic CIWS 0-2 hr Forecast, and the probabilistic National Convective Weather Forecast, Convective SIGMET and the Collaborative Convective Forecast Product.